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MetroNIDAZOLE (Systemic)

Pronunciation

Pronunciation

(met roe NYE da zole)

Index Terms

  • Benzoyl Metronidazole
  • Flagyl
  • Metronidazole Benzoate
  • Metronidazole Hydrochloride

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling. [DSC] = Discontinued product

Capsule, Oral:

Flagyl: 375 mg

Generic: 375 mg

Solution, Intravenous:

Metro: 500 mg (100 mL)

Generic: 500 mg (100 mL)

Solution, Intravenous [preservative free]:

Generic: 500 mg (100 mL [DSC])

Tablet, Oral:

Flagyl: 250 mg, 500 mg

Generic: 250 mg, 500 mg

Tablet Extended Release 24 Hour, Oral:

Flagyl ER: 750 mg

Brand Names: U.S.

  • Flagyl
  • Flagyl ER
  • Metro

Pharmacologic Category

  • Amebicide
  • Antibiotic, Miscellaneous
  • Antiprotozoal, Nitroimidazole

Pharmacology

After diffusing into the organism, interacts with DNA to cause a loss of helical DNA structure and strand breakage resulting in inhibition of protein synthesis and cell death in susceptible organisms

Absorption

Oral: Well absorbed

Distribution

To bile, seminal fluid, bone, liver, and liver abscesses, lung and vaginal secretions; crosses blood-brain barrier; saliva and CSF concentrations similar to those in plasma

Metabolism

Hepatic (30% to 60%) to several metabolites including an active hydroxyl metabolite which maintains activity ~30% to 65% of the parent compound (Lamp 1999)

Excretion

Urine (unchanged drug and metabolites: 60% to 80%; ~20% of total as unchanged drug); feces (6% to 15%)

Time to Peak

Serum: Oral: Immediate release: 1-2 hours; Extended release: ~5 hours

Half-Life Elimination

Neonates <7 days (Jager-Roman 1982): Within first week of life, more prolonged than with lower GA:

GA 28 to 30 weeks: 75.3 ± 16.9 hours

GA 32 to 35 weeks: 35.4 ± 1.5 hours

GA 36 to 40 weeks: 24.8 ± 1.6 hours

Neonates ≥7 days: ~22.5 hours (Upadhyaya 1988)

Children and Adolescents: 6 to 10 hours (Lamp 1999)

Adults: ~8 hours

Protein Binding

<20%

Special Populations: Renal Function Impairment

CrCl ≤65 mL/minute: Half-life: 18-32 hours (hydroxy metabolite [active]) (Lamp, 1999)

Special Populations: Hepatic Function Impairment

Half-life: 18.31 hours (mean) in one study (Lau, 1987)

According to Child-Pugh classification (Muscara, 1995):

Child-Pugh class A: ~10.7 hours

Child-Pugh class B: ~13.5 hours

Child-Pugh class C: ~21.5 hours

Use: Labeled Indications

Amebiasis: Oral immediate release tablet and capsule: Treatment of acute intestinal amebiasis (amebic dysentery) and amebic liver abscess

Limitations of use (oral immediate-release tablet, capsule and injection): When used for amebic liver abscess, may be used concurrently with percutaneous needle aspiration when it is clinically indicated

Anaerobic bacterial infections (caused by Bacteroides spp, including the B. fragilis group): Oral immediate-release tablet, capsule, and injection:

Bacterial septicemia: Treatment of bacterial septicemia (also caused by Clostridium spp)

Bone and joint infections: Treatment (adjunctive therapy) of bone and joint infections

CNS Infections: Treatment of CNS infections, including meningitis and brain abscess

Endocarditis: Treatment of endocarditis

Gynecologic infections: Treatment of gynecologic infections including endometritis, endomyometritis, tubo-ovarian abscess, or postsurgical vaginal cuff infection (also caused by Clostridium spp, Peptococcus spp, Peptostreptococcus spp, and Fusobacterium spp)

Intra-abdominal infections: Treatment of intra-abdominal infections, including peritonitis, intra-abdominal abscess and liver abscess (also caused by Clostridium spp, Eubacterium spp, Peptococcus spp, and Peptostreptococcus spp)

Lower respiratory tract infections: Treatment of lower respiratory tract infections, including pneumonia, empyema and lung abscess

Skin and skin structure infections: Treatment of skin and skin structure infections (also caused by Clostridium spp, Peptococcus spp, Peptostreptococcus spp, and Fusobacterium spp)

Bacterial vaginosis: Oral extended-release tablet: Treatment of bacterial vaginosis in nonpregnant women

Surgical prophylaxis (colorectal surgery): Injection: Preoperative, intraoperative, and postoperative prophylaxis to reduce the incidence of postoperative infection in patients undergoing elective colorectal surgery classified as contaminated or potentially contaminated.

Trichomoniasis: Oral immediate-release tablet, capsule, and injection: Treatment of infections caused by Trichomonas vaginalis, including treatment of asymptomatic sexual partners

Use: Unlabeled

Treatment of the following diseases: Balantidiasis; Clostridium difficile-associated diarrhea (CDAD); Crohn disease; Dientamoeba fragilis infections, giardiasis, Helicobacter pylori infections; periodontitis (aggressive disease), pouchitis (acute); surgical prophylaxis (oral for colorectal surgery and injection for other procedures); tetanus; urethritis

Prophylaxis: Prophylaxis of sexual assault victim (to treat trichomoniasis)

Contraindications

Hypersensitivity to metronidazole, nitroimidazole derivatives, or any component of the formulation; pregnant patients (first trimester) with trichomoniasis; use of disulfiram within the past 2 weeks; use of alcohol or propylene glycol-containing products during therapy or within 3 days of therapy discontinuation

Dosing: Adult

Amebiasis (acute dysentery): Oral: Immediate-release tablets and capsules: 750 mg every 8 hours for 5 to 10 days

Amebic liver abscess: Oral:

Immediate-release tablets: 500 to 750 mg every 8 hours for 5 to 10 days

Capsules: 750 mg every 8 hours for 5 to 10 days

Anaerobic infections (diverticulitis, peritonitis, cholangitis, or abscess): Oral (immediate release), IV: 500 mg every 6 hours (maximum: 4 g/day); Note: Initial: 1 g IV loading dose may be administered

Bacterial vaginosis or vaginitis due to Gardnerella, Mobiluncus: Oral: Tablet:

Immediate release (off-label use): 500 mg twice daily for 7 days (CDC [Workowski 2015])

Extended release: 750 mg once daily for 7 days

Intra-abdominal infection:

Manufacturer’s labeling: Oral (immediate release), IV: 500 mg every 6 hours (maximum: 4 g/day); Note: Initial: 1 g IV loading dose may be administered

Alternate dosing: Complicated, community-acquired, mild to moderate (in combination with cephalosporin or fluoroquinolone; off-label dosing): IV: 500 mg every 8 to 12 hours or 1.5 g every 24 hours for 4 to 7 days (provided source controlled) (Solomkin 2010)

Pelvic inflammatory disease (off-label dosing): Oral (immediate release):

Mild to moderately severe: 500 mg twice daily for 14 days (may be added to a combination of a third-generation parenteral cephalosporin and doxycycline) (CDC [Workowski 2015])

With tubo-ovarian abscess: 500 mg twice daily to complete at least 14 days of therapy (in combination with doxycycline following a parenteral therapy regimen)

Trichomoniasis (index case and sex partner): Oral:

Immediate-release tablets:

Manufacturer’s labeling: 250 mg every 8 hours for 7 days or 1 g twice daily for 2 doses (on same day) or 2 g as a single dose

Alternate dosing: 2 g as a single dose (preferred regimen) or 500 mg twice daily for 7 days (off-label dose) (CDC [Workowski 2015])

Capsules: 375 mg twice daily for 7 days

Trichomoniasis in HIV-infected women (off-label dose): Oral (immediate release): 500 mg twice daily for 7 days (CDC [Workowski 2015])

Trichomoniasis, persistent or recurrent (ie, treatment failure of nitroimidazole [eg metronidazole] single-dose therapy) (index case; treatment of sex partner; off-label dose): Oral (immediate release): 500 mg twice daily for 7 days. If this regimen also fails, consider 2 g once daily for 7 days (CDC [Workowski 2015])

Balantidiasis (off-label use): IV, Oral (immediate release): 750 mg 3 times daily for ≥5 days (Anagyrou 2003; Schuster 2008)

Bite wounds (animal/human) (off-label use) (IDSA [Stevens 2014]): Note: Use in combination with a second- or third-generation cephalosporin, levofloxacin, or sulfamethoxazole/trimethoprim for animal bites, or in combination with ciprofloxacin or levofloxacin for human bites.

Oral: 250 to 500 mg 3 times daily

IV: 500 mg every 8 hours

Clostridium difficile-associated diarrhea (CDAD) (off-label use):

Mild to moderate infection: Oral (immediate release): 500 mg 3 times daily for 10 to 14 days (Cohen 2010; Surawicz 2013)

Severe complicated infection (no abdominal distention): IV: 500 mg 3 times daily with oral vancomycin for 10 to 14 days (Surawicz 2013)

Severe complicated infection (with ileus, toxic colitis, and/or abdominal distention): IV: 500 mg 3 times daily with oral and rectal vancomycin for 10 to 14 days (Surawicz 2013)

Note: Recent guideline recommends converting to oral vancomycin therapy if the patient does not show a clear clinical response after 5 to 7 days of metronidazole therapy (Surawicz 2013)

Crohn disease (off-label use): Oral (immediate release): 10 to 20 mg/kg/day; long-term (eg, several months) safety has not been established (Lichtenstein 2009). Note: Reserved for mild to moderate disease in patients not responsive to sulfasalazine and/or who have colonic involvement (eg ileocolitis and colitis) (Lichtenstein 2009; Sutherland, 1991).

Dientamoeba fragilis infections (off-label use): Oral (immediate release): 500 to 750 mg 3 times daily for 10 days (CDC 2012)

Giardiasis (off-label use): Oral (immediate release): 250 to 500 mg 3 times daily for 5 to 10 days (Granados 2012)

Helicobacter pylori eradication (off-label use): Oral (immediate release):

Triple therapy: Metronidazole 500 mg twice daily for 10 to 14 days, in combination with clarithromycin and a proton pump inhibitor (Chey 2007)

Quadruple therapy: Metronidazole 250 mg 4 times daily for 10 to 14 days, in combination with bismuth subsalicylate, a tetracycline, and either ranitidine or a proton pump inhibitor (Chey 2007)

Periodontitis (associated with aggressive disease; off-label use): Oral (immediate release): 250 mg every 8 hours in combination with amoxicillin for 10 days; used in addition to scaling, root planing and pocket irrigation (Silva-Senem 2013)

Pouchitis (post ileal pouch-anal anastomosis, acute treatment; off-label use): Oral (immediate release): 400 to 500 mg three times daily for 7 days (Holubar 2010; Wall 2011)

Prophylaxis against sexually-transmitted diseases following sexual assault (off-label use): Oral (immediate release): 2 g as a single dose in combination with ceftriaxone and azithromycin (CDC [Workowski 2015])

Skin and soft tissue necrotizing infections (off-label use): IV: 500 mg every 6 hours, in combination with cefotaxime for empiric therapy of polymicrobial infections. Continue until further debridement is not necessary, patient has clinically improved, and patient is afebrile for 48 to 72 hours (IDSA [Stevens 2014]).

Surgical prophylaxis:

Manufacturer’s labeling: IV: 15 mg/kg 1 hour prior to surgical incision; followed by 7.5 mg/kg 6 and 12 hours after initial dose

Alternate dosing:

IV: 500 mg within 60 minutes prior to surgical incision in combination with other antibiotics (Bratzler 2013). Note: Considered a recommended agent for select procedures other than colorectal surgery (off-label use) (Bratzler 2013).

Oral (for colorectal surgical prophylaxis only; immediate release; off-label use): 1 g every 3 to 4 hours for 3 doses, starting after mechanical bowel preparation the afternoon and evening before the procedure with or without additional oral antibiotics and with an appropriate IV antibiotic prophylaxis regimen (Bratzler 2013).

Surgical site infections (intestinal or GU tract; axilla or perineum) (off-label use): IV: 500 mg every 8 hours; in combination with ceftriaxone, ciprofloxacin, or levofloxacin (IDSA [Stevens 2014]).

Tetanus (Clostridium tetani infection; off-label use): Oral (immediate release): 500 mg every 6 hours for 7 to 10 days in combination with supportive therapy (Ahmadsyah, 1985)

Urethritis, nongonococcal (recurrent or persistent urethritis in men who have sex with women and who live in regions where T. vaginalis is prevalent; off-label use): Oral (immediate release): 2 g as a single dose. Note: Compliance with initial regimen and lack of re-exposure to an untreated sex partner should be excluded prior to use (CDC [Workowski 2015])

Dosing: Geriatric

Refer to adult dosing.

Dosing: Pediatric

Infants, Children, and Adolescents:

Amebiasis: Oral: 35 to 50 mg/kg/day in divided doses every 8 hours for 7 to 10 days (Red Book [AAP 2012])

Trichomoniasis: Oral: 15 mg/kg/day in divided doses every 8 hours for 7 days (Red Book [AAP 2012])

Anaerobic infections (off-label dosing):

Oral: 30 to 50 mg/kg/day in divided doses every 8 hours (maximum: 2,250 mg/day) (Red Book [AAP 2012])

IV: 22.5 to 40 mg/kg/day in divided doses every 8 hours (maximum: 1,500 mg/day) (Red Book [AAP 2012])

Balantidiasis (off-label use): Oral: 35 to 50 mg/kg/day in 3 divided doses for 5 days (Red Book [AAP 2012]; Schuster 2008)

Clostridium difficile-associated diarrhea (CDAD; off-label use): Oral: 30 mg/kg/day divided every 6 hours for ≥10 days (maximum: 2 g/day) (Red Book [AAP 2012]; Schutze 2013). Note: Recommended agent for the initial treatment of mild to moderate disease and for first relapse (Red Book [AAP 2012]; Schutze 2013).

Giardiasis (off-label use): Oral: 15 mg/kg/day in divided doses every 8 hours for 5 to 10 days (Granados 2012; Red Book [AAP 2012])

Helicobacter pylori eradication (off-label use): Oral: 20 mg/kg/day in 2 divided doses for 10 to 14 days in combination therapy with amoxicillin and either a proton pump inhibitor or bismuth subsalicylate daily or 20 mg/kg/day in 2 divided doses on days 6 through 10 in combination therapy with a proton pump inhibitor and clarithromycin (after treatment with amoxicillin and a proton pump inhibitor for days 1 through 5) (maximum: 1 g/day) (Koletzko 2011)

Skin and soft tissue necrotizing infections (off-label use): IV: 7.5 mg/kg every 6 hours, in combination with cefotaxime for empiric therapy of polymicrobial infections. Continue until further debridement is not necessary, patient has clinically improved, and patient is afebrile for 48 to 72 hours (IDSA [Stevens 2014]).

Surgical (preoperative) prophylaxis (off-label use):

Infants <1,200 g: IV: 7.5 mg/kg within 60 minutes prior to surgical incision in combination with other antibiotics (Bratzler 2013).

Infants ≥1,200 g and Children ≥1 year:

IV: 15 mg/kg within 60 minutes prior to surgical incision in combination with other antibiotics (maximum: 500 mg per dose) (Bratzler 2013).

Oral (for colorectal surgical prophylaxis only): 15 mg/kg (maximum: 1,000 mg) every 3 to 4 hours for 3 doses, starting after mechanical bowel preparation the afternoon and evening before the procedure, with or without additional oral antibiotics and with an appropriate IV antibiotic prophylaxis regimen (Bratzler 2013).

Tetanus (Clostridium tetani infection, off-label use): Oral, IV: 30 mg/kg per day in divided doses every 6 hours for 10 to 14 days in combination with tetanus immune globulin and supportive therapy (maximum: 4 g/day) (Red Book [AAP 2012])

Adolescents: Oral:

Pelvic inflammatory disease (off-label dosing): Refer to adult dosing

Prophylaxis against sexually-transmitted diseases following sexual assault (off-label use): Refer to adult dosing.

Vaginal infections:

Vaginitis: (Trichomonas vaginalis; off-label use): 2 g as a single dose (Red Book [AAP 2012])

Vaginosis (bacterial; off-label use): 500 mg twice daily for 7 days (Red Book [AAP 2012])

Dosing: Renal Impairment

Manufacturer’s labeling:

Mild, moderate, or severe impairment: There are no dosage adjustments provided in the manufacturer’s labeling; however, decreased renal function does not alter the single-dose pharmacokinetics

End-stage renal disease (ESRD) requiring dialysis: Metronidazole metabolites may accumulate; monitor for adverse events. Accumulated metabolites may be rapidly removed by dialysis:

Intermittent hemodialysis (IHD): If administration cannot be separated from hemodialysis, consider supplemental dose following hemodialysis.

Peritoneal dialysis (PD): No dosage adjustment necessary.

Alternate dosing:

Intermittent hemodialysis (IHD) (administer after hemodialysis on dialysis days): Dialyzable (50% to 100%): 500 mg every 8 to 12 hours. Note: Dosing regimen highly dependent on clinical indication (trichomoniasis vs C. difficile colitis) (Heintz 2009). Note: Dosing dependent on the assumption of thrice weekly, complete IHD sessions.

Continuous renal replacement therapy (CRRT) (Heintz 2009; Trotman 2005): Drug clearance is highly dependent on the method of renal replacement, filter type, and flow rate. Appropriate dosing requires close monitoring of pharmacologic response, signs of adverse reactions due to drug accumulation, as well as drug concentrations in relation to target trough (if appropriate). The following are general recommendations only (based on dialysate flow/ultrafiltration rates of 1 to 2 L/hour and minimal residual renal function) and should not supersede clinical judgment:

CVVH/CVVHD/CVVHDF: 500 mg every 6 to 12 hours (or per clinical indication; dosage reduction generally not necessary)

Dosing: Hepatic Impairment

Manufacturer’s labeling:

Mild or moderate impairment (Child-Pugh class A or B): No dosage adjustment necessary; use with caution and monitor for adverse events

Severe impairment (Child-Pugh class C):

Extended-release tablets: Use is not recommended.

Immediate-release capsules:

Amebiasis: 375 mg 3 times daily

Trichomoniasis: 375 mg once daily

Immediate-release tablets, injection: Reduce dose by 50%

Alternate dosing: The pharmacokinetics of a single oral 500 mg dose were not altered in patients with cirrhosis; initial dose reduction is therefore not necessary (Daneshmend, 1982). In one study of IV metronidazole, patients with alcoholic liver disease (with or without cirrhosis), demonstrated a prolonged elimination half-life (eg, ~18 hours). The authors recommended the dose be reduced accordingly (clearance was reduced by ~62%) and the frequency may be prolonged (eg, every 12 hours instead of every 6 hours) (Lau, 1987). In another single IV dose study using metronidazole metabolism to predict hepatic function, patients classified as Child-Pugh class C demonstrated a half-life of ~21.5 hours (Muscara, 1995).

Extemporaneously Prepared

A 50 mg/mL oral suspension may be made with tablets and a 1:1 mixture of Ora-Sweet and Ora-Plus. Crush twenty-four 250 mg tablets in a mortar and reduce to a fine powder. Add small portions of the vehicle and mix to a uniform paste; mix while adding the vehicle in incremental portions to almost 120 mL; transfer to a calibrated bottle, rinse mortar with vehicle, and add quantity of vehicle sufficient to make 120 mL. Label "shake well". Stable for 60 days at room temperature or refrigerated (Allen, 1996).

Administration

IV: Infuse intravenously over 30 to 60 minutes. Avoid contact of drug solution with equipment containing aluminum.

Oral: Immediate-release tablets and capsules may be administered with food to minimize stomach upset. Extended-release tablets should be administered on an empty stomach (1 hour before or 2 hours after meals); do not split, crush, or chew.

Dietary Considerations

Immediate-release tablets and capsules may be administered with food to minimize stomach upset. Extended-release tablets should be taken on an empty stomach (1 hour before or 2 hours after meals).

Sodium: Injectable dosage form may contain sodium.

Ethanol: Use of ethanol is contraindicated during therapy and for 3 days after therapy discontinuation.

Compatibility

Stable in D5W, LR, NS.

Y-site administration: Incompatible with amphotericin B cholesteryl sulfate complex, aztreonam, filgrastim, pemetrexed. Variable (consult detailed reference): Caspofungin, ceftriaxone, meropenem, pantoprazole, warfarin.

Storage

Oral:

Extended release: Store at 25°C (77°F); excursions are permitted between 15°C and 30°C (59°F and 86°F).

Immediate release: Store at 15°C to 25°C (59°F to 77°F). Protect the tablets from light.

Injection: Store at 20°C to 25°C (68°F to 77°F). Protect from light. Avoid excessive heat. Do not refrigerate. Do not remove unit from overwrap until ready for use. Discard unused solution.

Drug Interactions

Alcohol (Ethyl): MetroNIDAZOLE (Systemic) may enhance the adverse/toxic effect of Alcohol (Ethyl). A disulfiram-like reaction may occur. Avoid combination

BCG (Intravesical): Antibiotics may diminish the therapeutic effect of BCG (Intravesical). Avoid combination

BCG Vaccine (Immunization): Antibiotics may diminish the therapeutic effect of BCG Vaccine (Immunization). Monitor therapy

Busulfan: MetroNIDAZOLE (Systemic) may increase the serum concentration of Busulfan. Management: The toxic effects of busulfan may be greatly increased with concomitant use of metronidazole. This combination should probably be avoided when possible. If these agents must be used together, increased monitoring for busulfan toxicity is recommended. Consider therapy modification

Capecitabine: MetroNIDAZOLE (Systemic) may increase serum concentrations of the active metabolite(s) of Capecitabine. Monitor therapy

Carbocisteine: MetroNIDAZOLE (Systemic) may enhance the adverse/toxic effect of Carbocisteine. Specifically, metronidazole may enhance adverse effects of alcohol that is present in liquid formulations of carbocisteine-containing products. Avoid combination

Cholera Vaccine: Antibiotics may diminish the therapeutic effect of Cholera Vaccine. Avoid combination

Disulfiram: May enhance the adverse/toxic effect of MetroNIDAZOLE (Systemic). Avoid combination

Dronabinol: MetroNIDAZOLE (Systemic) may enhance the adverse/toxic effect of Dronabinol. Specifically, metronidazole may produce severe intolerance to the alcohol contained in the dronabinol oral solution. Consider therapy modification

Fluorouracil (Systemic): MetroNIDAZOLE (Systemic) may increase the serum concentration of Fluorouracil (Systemic). Monitor therapy

Fosphenytoin: May decrease the serum concentration of MetroNIDAZOLE (Systemic). MetroNIDAZOLE (Systemic) may increase the serum concentration of Fosphenytoin. Monitor therapy

Highest Risk QTc-Prolonging Agents: QTc-Prolonging Agents (Indeterminate Risk and Risk Modifying) may enhance the QTc-prolonging effect of Highest Risk QTc-Prolonging Agents. Management: Avoid such combinations when possible. Use should be accompanied by close monitoring for evidence of QT prolongation or other alterations of cardiac rhythm. Consider therapy modification

Lactobacillus and Estriol: Antibiotics may diminish the therapeutic effect of Lactobacillus and Estriol. Monitor therapy

Lopinavir: MetroNIDAZOLE (Systemic) may enhance the adverse/toxic effect of Lopinavir. Specifically, the combination of metronidazole and lopinavir/ritonavir solution, which contains 42% alcohol, may result in a disulfiram-like reaction. MetroNIDAZOLE (Systemic) may enhance the arrhythmogenic effect of Lopinavir. Management: Avoid the concomitant use of lopinavir/ritonavir and metronidazole if possible. If these agents are used concomitantly, monitor for QTc prolongation/arrhythmia and if the lopinavir/ritonavir solution is used, development of a disulfiram-like reaction. Consider therapy modification

Mebendazole: May enhance the adverse/toxic effect of MetroNIDAZOLE (Systemic). Particularly the risk for Stevens-Johnson syndrome or toxic epidermal necrolysis may be increased. Avoid combination

MiFEPRIStone: May enhance the QTc-prolonging effect of QTc-Prolonging Agents (Indeterminate Risk and Risk Modifying). Management: Though the drugs listed here have uncertain QT-prolonging effects, they all have some possible association with QT prolongation and should generally be avoided when possible. Consider therapy modification

Moderate Risk QTc-Prolonging Agents: QTc-Prolonging Agents (Indeterminate Risk and Risk Modifying) may enhance the QTc-prolonging effect of Moderate Risk QTc-Prolonging Agents. Monitor therapy

Mycophenolate: MetroNIDAZOLE (Systemic) may decrease the serum concentration of Mycophenolate. Specifically, metronidazole may decrease concentrations of the active metabolite of mycophenolate. Monitor therapy

PHENobarbital: May decrease the serum concentration of MetroNIDAZOLE (Systemic). Monitor therapy

Phenytoin: May decrease the serum concentration of MetroNIDAZOLE (Systemic). MetroNIDAZOLE (Systemic) may increase the serum concentration of Phenytoin. Monitor therapy

Primidone: May decrease the serum concentration of MetroNIDAZOLE (Systemic). Monitor therapy

Ritonavir: May enhance the adverse/toxic effect of MetroNIDAZOLE (Systemic). Specifically, the combination of ritonavir oral solution or ritonavir soft gelatin capsule, both of which contain alcohol, and metronidazole may result in a disulfiram-like reaction. Avoid combination

Sodium Picosulfate: Antibiotics may diminish the therapeutic effect of Sodium Picosulfate. Management: Consider using an alternative product for bowel cleansing prior to a colonoscopy in patients who have recently used or are concurrently using an antibiotic. Consider therapy modification

Tegafur: MetroNIDAZOLE (Systemic) may increase serum concentrations of the active metabolite(s) of Tegafur. Monitor therapy

Tipranavir: MetroNIDAZOLE (Systemic) may enhance the adverse/toxic effect of Tipranavir. A disulfiram-like reaction may occur due to the alcohol contained in tipranavir capsules. Monitor therapy

Typhoid Vaccine: Antibiotics may diminish the therapeutic effect of Typhoid Vaccine. Only the live attenuated Ty21a strain is affected. Management: Vaccination with live attenuated typhoid vaccine (Ty21a) should be avoided in patients being treated with systemic antibacterial agents. Use of this vaccine should be postponed until at least 3 days after cessation of antibacterial agents. Consider therapy modification

Vitamin K Antagonists (eg, warfarin): MetroNIDAZOLE (Systemic) may increase the serum concentration of Vitamin K Antagonists. Management: Consider alternatives to concomitant therapy with these agents. If concomitant therapy cannot be avoided, consider reducing the dose of the vitamin K antagonist and monitor for increased INR/bleeding. Consider therapy modification

Test Interactions

May interfere with AST, ALT, triglycerides, glucose, and LDH testing

Adverse Reactions

>10%:

Central nervous system: Headache (18%)

Gastrointestinal: Nausea (10% to 12%)

Genitourinary: Vaginitis (15%)

1% to 10%:

Central nervous system: Metallic taste (9%), dizziness (4%)

Dermatologic: Genital pruritus (5%)

Gastrointestinal: Abdominal pain (4%), diarrhea (4%), xerostomia (2%)

Genitourinary: Dysmenorrhea (3%), urine abnormality (3%), urinary tract infection (2%)

Infection: Bacterial infection (7%), candidiasis (3%)

Respiratory: Flu-like symptoms (6%), upper respiratory tract infection (4%), pharyngitis (3%), sinusitis (3%)

Frequency not defined:

Cardiovascular: Flattened T-wave on ECG, flushing, syncope

Central nervous system: Aseptic meningitis, ataxia, brain disease, confusion, convulsions, depression, disulfiram-like reaction (with alcohol), dysarthria, insomnia, irritability, peripheral neuropathy, psychosis, seizure, sensation of pelvic pressure, vertigo

Dermatologic: Erythematous rash, pruritus, Stevens-Johnson syndrome, toxic epidermal necrolysis, urticaria

Endrocrine & metabolic: Decreased libido

Gastrointestinal: Abdominal cramps, abdominal distress, anorexia, constipation, dyspareunia, epigastric distress, glossitis, hairy tongue, hiccups, pancreatitis (rare), proctitis, stomatitis, vomiting

Genitourinary: Cystitis, dark urine (rare), dysuria, urinary incontinence, vaginal dryness, vulvovaginal candidiasis

Hematologic & oncologic: Leukopenia (reversible), thrombocytopenia (reversible, rare)

Immunologic: Serum sickness-like reaction (joint pains)

Local: Inflammation at injection site (IV)

Neuromuscular & skeletal: Arthralgia, weakness

Ophthalmic: Optic neuropathy

Renal: Polyuria

Respiratory: Nasal congestion, rhinitis

Miscellaneous: Fever, lesion (central nervous system, reversible)

ALERT: U.S. Boxed Warning

Carcinogenic:

Metronidazole has been shown to be carcinogenic in mice and rats. Unnecessary use of the drug should be avoided. Its use should be reserved for the conditions for which this drug is indicated.

Warnings/Precautions

Concerns related to adverse effects:

• Carcinogenic: [U.S. Boxed Warning]: Possibly carcinogenic based on animal data. Reserve use for conditions described in Use; unnecessary use should be avoided.

• CNS effects: Aseptic meningitis (symptoms may occur within hours of a dose), encephalopathy (cerebellar toxicity with ataxia, dizziness, dysarthria and/or CNS lesions), seizures, peripheral neuropathy (including extremity numbness and paresthesia) and optic neuropathy have been reported especially with increased doses and chronic treatment; monitor and consider discontinuation of therapy if signs/symptoms occur. Symptoms associated with aseptic meningitis and encephalopathy generally resolve following therapy discontinuation. Use with caution in patients with a history of seizure disorder.

• Infection: Prolonged use may result in fungal or bacterial superinfection, including C. difficile-associated diarrhea (CDAD) and pseudomembranous colitis; CDAD has been observed >2 months postantibiotic treatment. Candidiasis infection (known or unknown) may be more prominent during metronidazole treatment, antifungal treatment required.

Disease-related concerns:

• Blood dyscrasias: Use with caution in patients with or history of blood dyscrasias; leukopenia has occurred. Monitor CBC with differential at baseline, during and after treatment.

• Hepatic impairment: Use with caution in patients with severe liver impairment due to potential accumulation; dosage adjustment is recommended in these patients.

• Renal impairment: Use with caution in patients with end-stage renal disease (ESRD) due to potential accumulation. Accumulated metabolites may be rapidly removed by hemodialysis; supplemental doses may be needed.

Concurrent drug therapy issues:

• Drug-drug interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.

Special Populations:

• Elderly: Use with caution; dosage adjustment may be required based on renal and/or hepatic function.

Dosage-form specific issues:

• Extended-release tablets: Do not use in patients with severe hepatic impairment (Child-Pugh class C) unless benefit outweighs risk.

• Use injection with caution in patients with heart failure, edema or other sodium retaining states, including corticosteroid treatment. In patients receiving continuous nasogastric secretion aspiration, sufficient metronidazole may be removed in the aspirate to cause a reduction in serum levels.

Other warnings/precautions:

• Appropriate use: Guidelines recommend the use of oral metronidazole for initial treatment of mild to moderate C. difficile infection and the use of oral vancomycin for initial treatment of severe C. difficile infection (with or without IV metronidazole depending on the presence of complications). May treat recurrent mild to moderate infection once with oral metronidazole; avoid use beyond first reoccurrence. (Cohen, 2010; Surawicz, 2013).

• Ethanol use: Abdominal cramps, nausea, vomiting, headaches, and flushing have been reported with oral and injectable metronidazole and concomitant alcohol consumption (disulfiram-like reactions); avoid alcoholic beverages or products containing propylene glycol during oral or injectable therapy and for at least 3 days after oral therapy.

Monitoring Parameters

Monitor CBC with differential at baseline and after prolonged or repeated courses of therapy. Closely monitor elderly patients and patients with severe hepatic impairment or ESRD for adverse reactions. Observe patients carefully if neurologic symptoms occur and consider discontinuation of therapy.

Pregnancy Risk Factor

B

Pregnancy Considerations

Use of metronidazole during the first trimester of pregnancy is contraindicated by the manufacturer for the treatment of trichomoniasis. Metronidazole crosses the placenta. Cleft lip with or without cleft palate has been reported following first trimester exposure to metronidazole; however, most studies have not shown an increased risk of congenital anomalies or other adverse events to the fetus following maternal use during pregnancy. Because metronidazole was carcinogenic in some animal species, concern has been raised whether metronidazole should be used during pregnancy. Available studies have not shown an increased risk of infant cancer following metronidazole exposure during pregnancy; however, the ability to detect a signal for this may have been limited.

Metronidazole pharmacokinetics are similar between pregnant and nonpregnant patients (Amon 1981; Visser 1984; Wang 2011). Bacterial vaginosis has been associated with adverse pregnancy outcomes; metronidazole is recommended for the treatment of symptomatic bacterial vaginosis in pregnant patients (CDC [Workowski 2015]). Vaginal trichomoniasis has been also associated with adverse pregnancy outcomes; use of metronidazole for this indication during the first trimester is contraindicated by the manufacturer; however, some guidelines note treatment can be given at any stage of pregnancy (CDC [Workowski 2015]). Metronidazole may also be used for the treatment of giardiasis in pregnant women (some sources recommend second and third trimester administration only) (HHS [OI adult 2015]; Gardner 2001) and symptomatic amebiasis during pregnancy (HHS [OI adult 2015]; Li 1996). Short courses may be used for the treatment of pouchitis or perianal disease in pregnant women with inflammatory bowel disease (avoid use in the first trimester) (van der Woude 2015).The use of other agents is preferred when treatment is needed during pregnancy for Clostridium difficile (Surawicz 2013) or Helicobacter pylori (Mahadevan 2006). Consult current guidelines for appropriate use in pregnant women.

Patient Education

• Discuss specific use of drug and side effects with patient as it relates to treatment. (HCAHPS: During this hospital stay, were you given any medicine that you had not taken before? Before giving you any new medicine, how often did hospital staff tell you what the medicine was for? How often did hospital staff describe possible side effects in a way you could understand?)

• Patient may experience nausea, vomiting, diarrhea, constipation, headache, lack of appetite, or metallic taste. Have patient report immediately to prescriber change in balance, difficulty speaking, seizures, redness or white patches in mouth, vision changes, burning or numbness feeling, irritation at injection site, or signs of aseptic meningitis (headache, fever, chills, severe nausea or vomiting, stiff neck, rash, bright lights that bother eyes, fatigue, or illogical thinking) (HCAHPS).

• Educate patient about signs of a significant reaction (eg, wheezing; chest tightness; fever; itching; bad cough; blue skin color; seizures; or swelling of face, lips, tongue, or throat). Note: This is not a comprehensive list of all side effects. Patient should consult prescriber for additional questions.

Intended Use and Disclaimer: Should not be printed and given to patients. This information is intended to serve as a concise initial reference for healthcare professionals to use when discussing medications with a patient. You must ultimately rely on your own discretion, experience and judgment in diagnosing, treating and advising patients.

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